The present invention relates to a CRT color video printer for printing a video image displayed on a black-and-white CRT on a photographic material in a three color sequential exposure by the use of a printing lens, and more particularly to a CRT color video printer for printing a video image displayed on a black-and-white CRT onto a photographic material by the use of a zoom lens in which chromatic aberrations in magnification of the printing lens can be corrected.
CRT color video printers use black-and-white CRTs to sequentially display black-and-white images in a brightness pattern corresponding to three color images which in turn are changed to three monochromatic images through three color filters. The use of black-and-white CRTs is useful for improving resolution. The three monochromatic images are printed on a photographic material such as a color photographic paper in a three color sequential exposure. Such a CRT color video printer is disclosed in, for example, Japanese Patent Unexamined Publication No. 58-31330.
In such CRT color video printers, as is disclosed in, for example, Japanese Patent Unexamined Publication No. 62-66246, it increasingly becomes popular to use a zoom lens having a relatively high zooming ratio as a printing lens in order to make various sizes of prints.
With a printing lens having a high magnification or a zoom lens available at a high magnification, a hard copy or print sometimes shows blurred colors and color registration errors. These color defects are caused due to lateral and longitudinal chromatic aberrations which are different depending upon colors and magnifications of the printing lens. In the extreme case, a deviation of approximately two percent of the overall height of an image arises between, for example, red and blue images. For example, the peripheral deviation may be approximately 2 mm for an image having an overall height of about 100 mm. Such deviations lead to hard copies of inferior image quality.
The changes of magnification due to chromatic aberrations can be eliminated or reduced by using several lenses in combination. But the provision of a plurality of lenses is very expensive and therefore increases the manufacturing cost of the CRT color video printer.